Experimental investigations were made on the effects of the addition of boric acid on the rate of deposition in various sorts of electroless nickel and cobalt plating baths containing a hypophosphite as a reducing agent.
Furthermore, the action of boric acid for promoting the deposition rate was evaluated in caustic alkaline tartrate cobalt plating solution which was remarkably affected by boric acid.
As the results, the following conclusions were reached.
1) Remarkable promoting effects of boric acid were observed in both nickel and cobalt plating baths containing only hydroxy-carboxylic acid such as citric or tartaric acide.
2) Cobalt tartrate complex dissolved in weak acid solution was converted into a type of less reducible complex in alkaline solution.
3) The relationship between the deposition rate and pH of bath was illustrated by the dependence of reducing force of a hypophosphite on pH and the above conversion of the complex in the solution.
4) The addition of boric acid to the plating solution promoted the plating reaction in the bath by the aid of its buffer action and complex forming ability.